Reference sources like these will guide you through the recent scholarly thinking on a topic and then point you to related primary and secondary sources.
Combining the best features of an annotated bibliography and a high-level encyclopedia, this resource guides researchers to the best available scholarship.
From their website
This unique historical reference compendium allows instant access to the renowned texts of the Cambridge Histories series. With access to the most up to date and authoritative scholarly content, Cambridge Histories Online is an invaluable resource, for undergraduates, graduates, lecturers and researchers alike.
All the available volumes are grouped into topics, making it quick and easy to search and browse through an array of historical subject areas. The extensive bibliographic referencing and other leading functionality, enhances usability and makes this resource ideal for any type of historical research.
The Oxford Dictionary of the Middle Ages is a reference resource for all key aspects of European history, society, religion, and culture from circa 500 CE to circa 1500 CE. Relevant aspects of the Byzantine Empire, the Islamic dynasties, and Asiatic peoples such as the Avars and the Mongols are also included in this comprehensive work. It includes over 5,000 A-Z entries, written by more than 800 international scholars, covering the whole geographical extent of the European Middle Ages and balanced treatments of sixteen topics centrally important to the study of the period. Each entry includes an up-to-date bibliography to guide further reading and research.